Phase change medium erasable at low speed and recordable at high speed and a driving device for such a medium

ABSTRACT

A phase change medium, a device and a method for driving a phase change medium are proposed that allow writing at high speed and erasing at low speed. The proposed low-speed erasing option must be seen as a formatting option that can be applied to the whole medium (or to part of the medium) so as to put the medium (or part of the medium) back to a virgin state. With the invention, direct overwriting of data is not possible: the data have first to be erased at low speed before new data can be written on the medium at high speed. According to the invention, the medium is rotated at a linear velocity that depends on the selected operating mode, the linear velocity applied in the writing mode being much higher than said maximum crystalline velocity, and the linear velocity applied in said erasing mode being equal to or lower than said maximum crystalline velocity. Application: DVD+R high-speed.

FIELD OF THE INVENTION

The present invention relates to a phase-change optical storage medium,to a device for driving a phase-change optical storage medium and to amethod for driving a phase-change optical storage medium.

Phase change optical storage media have a layer made of a material thatis initially in an amorphous state and that is put in a crystallinestate during the manufacturing process. Data are written on a phasechange medium by locally heating the medium to a temperature at which itchanges from the crystalline state to the amorphous state, thus creatingamorphous marks with a different reflectance than the surroundingcrystalline area.

A change from the crystalline state to the amorphous state can beachieved at high speed, which makes such media very attractive forapplications requiring high storage densities and high recording speed.

Typically, a phase change medium that is compliant with the DVD+Rstandard can be written at a speed up to 16× where x is the speed atwhich the medium is read referred to as reference speed (DVD+R is theabbreviate for Digital Versatile Disc+R where R stands for Recordable).

TECHNOLOGICAL BACKGROUND OF THE INVENTION

As mentioned in EP patent 0286406 B1, phase change media are physicallyrewritable because re-crystallization of amorphous marks can be achievedby appropriate heating. However as further stated in EP patent 0286406B1, changes from the amorphous state back to the crystalline statecannot be achieved at high speed with conventional phase change media.EP patent 0286406 B1 proposes a phase change medium which recordinglayer is made of a new material. With this new material, both recordingand erasing can be achieved at high speed.

High-speed rewritable phase change media of the type described in EPpatent 0286406 are directed to applications for which a high-speederasing capability is needed.

An object of the invention is to propose a cost-effective solution forapplications that require a high-speed recording capability but forwhich a truly rewritable capability is not needed.

SUMMARY OF THE INVENTION

This is achieved with a device as claimed in any of the claims 1 to 6,with a medium as claimed in claim 7, and with a method as claimed inclaim 8.

A device and a method according to the invention are intended fordriving a phase-change medium having a layer made of a material capableof changing locally between an amorphous state and a crystalline state,said material being characterized by a maximum crystalline velocityabove which change from said amorphous state to said crystalline statecannot be achieved.

A device according to the invention comprises:

a user interface through which a user can select an operating modeamongst a plurality of operating modes including a writing mode forwriting data on said medium by locally changing said material from saidcrystalline state to said amorphous state and an erasing mode forerasing data written on said medium by locally changing said materialback from said amorphous state to said crystalline state,

means for producing a laser beam for scanning said medium,

means for controlling the power of said laser beam depending on theselected operating mode, and

means for rotating said medium at a linear velocity that depends on theselected operating mode, the linear velocity applied in said writingmode being much higher than said maximum crystalline velocity, and thelinear velocity applied in said erasing mode being equal to or lowerthan said maximum crystalline velocity.

A method according to the invention comprises the steps of:

reading a user selection amongst a plurality of available operatingmodes including a writing mode for writing data on said medium bylocally changing said material from said crystalline state to saidamorphous state and an erasing mode for erasing data written on saidmedium by locally changing said material back from said amorphous stateto said crystalline state,

producing a laser beam for scanning said medium,

controlling the power of said laser beam depending on the selectedoperating mode, and

rotating said medium at a linear velocity that depends on the selectedoperating mode, the linear velocity applied in said writing mode beingmuch higher than said maximum crystalline velocity, and the linearvelocity applied in said erasing mode being equal to or lower than saidmaximum crystalline velocity.

A phase-change write-once read-many medium according to the inventionhas:

a) a layer made of a material capable of changing locally between anamorphous state and a crystalline state when heated by a laser having anappropriate power while said medium is rotated at an appropriate linearvelocity, said material been characterized by a maximum crystallinevelocity above which change from said amorphous state to saidcrystalline state cannot be achieved,

b) a wobbled track which wobble carries medium-related information, saidmedium-related information comprising the value of:

the power and the linear velocity, referred to as writing power andwriting linear velocity, to be used for locally changing said materialfrom said crystalline state to said amorphous state,

the power and the linear velocity, referred to as erasing power anderasing linear velocity, to be used for locally changing said materialfrom said amorphous state to said crystalline state,

wherein said writing speed is much higher than said maximum crystallinevelocity and said erasing speed is not higher than said maximumcrystalline velocity.

The inventors of the present patent application have recognized that theconventional phase change technology is an appropriate solution forapplications that require a high-speed writing capability but for whicha truly rewritable capability is not needed. An example of such anapplication is the duplication of a video content from a sketch that wassuccessfully tested.

The inventors have also recognized that Write-Once Read-Many (WORM)media have the drawback that when the data written on the medium becomeobsolete or when the writing operation has failed, the medium cannot bere-used.

Therefore a phase change medium, a device and a method for driving aphase change medium are proposed that allow writing at high speed anderasing at low speed. The proposed low-speed erasing option must be seenas a formatting option that can be applied to the whole medium (or topart of the medium) so as to put the medium (or part of the medium) backto a virgin state. With the proposed phase change medium, driving deviceand driving method, direct overwriting of data is not possible. The datahave first to be erased at low speed before new data can be written onthe medium at high speed. Therefore the proposed medium is not trulyrewritable.

The proposed invention is of great interest for the end user because itprovides him/her with a relatively cheap medium with high-speedrecording capability, well adapted to most consumer applications, whilegiving him/her the option of formatting the medium when needed. Forinstance, the proposed invention will be advantageously used for DVD+Rhigh-speed applications.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are further described withreference to the following drawings:

FIG. 1 is a schematic representation of an example of medium accordingto the invention;

FIG. 2 is a schematic block diagram of an example of device according tothe invention;

FIG. 3 is a block diagram of a method according to the invention ofdriving a recordable medium.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 shows a medium 1, FIG. 1A being a plane view, FIG. 1B showing asmall part in a sectional view taken on line b-b, and FIG. 1B showing aportion 2 of the medium 1 in a larger scale. The medium 1 is a dischaving tracks forming each a 360° turn of a spiral line 3. Each trackcomprises a groove 4 and a land 5. For the purpose of recording data,the medium 1 has a recording layer 6, which is deposited on atransparent substrate 7 and which is covered by a protective coating 8.The data are recorded on the grooves 4. The tracks are scanned by alaser beam that enters the medium 1 through the substrate 7. The trackshave a continuous sinusoidal deviation from their average centreline.This sinusoidal deviation is referred to as wobble. In some standardsthe wobble is modulated to carry information. For instance in DVD+R thewobble is phase-modulated.

The medium is a phase change medium which means that the recording layer6 is made of a material capable of changing locally between an amorphousstate and a crystalline state. Data are written by locally heating themedium to a temperature at which it changes from the crystalline stateto the amorphous state, thus creating amorphous marks with a differentreflectance than the surrounding crystalline area. Conversely, data areerased by locally heating the medium to a temperature at which itchanges from the amorphous state back to the crystalline state.

The material of the recording layer 6 is characterized by a maximumcrystalline velocity above which change from said amorphous state tosaid crystalline state cannot be achieved.

FIG. 2 shows an example of a device 10 according to the invention fordriving the medium 1. The device 10 comprises inter alias an opticalunit 20, a bus 22, a microprocessor assembly 24, a user interface 26 asource encoder/decoder 28, a channel decoder 30, a channel encoder 32, aservo block 34, a motor control unit 35 and a wobble processing block36. The source encoder/decoder 28 is coupled to a host system 37 (by wayof example the host system 37 can be a PC, an audio player, a videolayer . . . ). The microprocessor assembly 24, the user interface 26,the source encoder/decoder 28, the channel decoder 30, the channelencoder 32, the servo block 34, the motor control unit 35 and the wobbleprocessing block 36 are connected to the bus 22.

The user interface 26 is designed so as to allow a user to select anoperating mode amongst a plurality of operating modes including:

a writing mode in which data provided by the host system 37 are writtenon the medium-1 by locally changing the material of the recording layerfrom the crystalline state to the amorphous state, and

an erasing mode in which data written on the medium 1 are erased bylocally changing the material of the recording layer from the amorphousstate back to the crystalline state.

Advantageously a reading mode is also available in which data written onthe medium 1 are read and delivered to the host system 37.

The optical unit 20 comprises a radiation source 38, for instance asemiconductor laser, generating a laser beam 41 that is directed onto atrack of the medium 1 by means of an optical system comprising, interalias, a focussing objective 42. The radiation source 38 is controlledby a radiation source control unit 40. The radiation source control unit40 is connected to the bus 22 and controls the power of the laser beam41 depending on the selected operating mode.

Typically, the radiation source control unit 40 drives the radiationsource 38 so that the produced laser beam 41 has:

a low power when the selected mode is the reading mode,

an intermediate power when the selected mode is the erasing mode,

a high power when the selected mode is the writing mode.

By way of example, the reading power is set to 0.7 mW±0.1 mW, thewriting power is set between 35 mW for a writing linear velocity equalto 16× (the writing power depends on the writing linear velocity), andthe erasing power is comprised between 5 mW and 10 mW.

The laser beam 41 produces a small spot 43 on the medium 1. For the spot43 to scan the tracks, the medium is rotated about a shaft 44 by a motor45. The motor 45 is controlled by the motor control unit 35. The motorcontrol circuit 35 adapts the linear velocity of the motor depending onthe selected operating mode. Conventionally, the linear velocity used inthe reading mode is referred to as reference speed and is noted x. Byway of example in the DVD+R standard the reading speed is x=3.49 m·s⁻¹.According to the invention:

the linear velocity used when the writing mode is selected is high (itcan be up to 16×);

the linear velocity used when the erasing mode is selected is low; it islower than the maximum crystalline velocity which depends on thematerial used for the recording layer 6; typically it is comprisedbetween 1× and 2.4×.

The laser beam 41 is reflected by the medium 1. The projected andreflected beams are separated one from the other by a beam splitter 46(for example a partially transparent mirror). The reflected radiationbeam 47 is passed on to a photo detector 50. The photo detector 50 has aradiation sensitive surface divided into a plurality of quadrants so asto generate a plurality of photocurrents. In FIG. 2, a four-quadrantsphoto detector is represented by way of example. This is notrestrictive. The four quadrants of the photo detector 50 carry referencenumber Q_(A), Q_(B), Q_(C) and Q_(D) respectively. They generate fourphotocurrents A, B, C, and D.

The four photocurrents A, B, C and D are forwarded to a pre-processingblock 60 responsible for generating:

several difference signals that are input to the servo block 34,

a wobble signal that is input to the wobble processing block 36, and

a data signal that is input to the channel decoder 30.

The servo block 34 is responsible for controlling the optical unit 20(including positioning the optical unit 20, focussing the laser beam 41,tracking the spiral line 3).

The wobble processing block 36 is responsible for processing the wobblesignal so as to recover the information carried by the wobble signal.

The channel decoder 30 is responsible for recovering the source-encodeddata from the data signal read by the optical unit 20. Thesource-encoded data are forwarded to the source encoder/decoder 28 inorder to be decoded. Eventually, the decoded data are delivered to thehost system 37.

The host system 37 can also provide data intended to be written on themedium 1. These data are encoded by the source encoder/decoder 28. Thesource-encoded data are then processed by the channel encoder 32. Thechannel-encoded data are applied to the radiation source control unit40.

As explained by reference to FIG. 1, the wobble signal is modulated soas to carry information (usually physical format information). In theDVD+R standard this information is called Address-in-Pregroove (orADIP). The ADIP notably comprises data about the reading and writingpower and the reading and writing linear velocity. Currently, there iscapacity for transmitting additional pieces of information compared tothe ADIP defined in the standard. In a preferred embodiment of theinvention, the erasing power and the erasing linear velocity aretransmitted as a part of the ADIP. This is advantageous because the ADIPinformation is included in the medium itself during the manufacturingstage. It doesn't have to be written on disc in a latter stage and itcan neither be removed nor modified.

Alternatively, the erasing power and the erasing linear velocity can bewritten in the information zone of the medium (that is in the recordablearea of the medium) or it can be stored in the device 10.

In order to allow for partial recording of the medium and subsequentappending of data to a partly recorded medium, the concept ofmulti-sessions has been introduced in many standards. For instance, amedium compliant with the DVD+R standard may contain a single session ora plurality of sessions. A table referred to as Table Of Content isstored at the beginning of the information zone and contains thenecessary information about recording on the disc (in particular, thelocation of the sessions).

In an advantageous embodiment the user interface 26 is designed so as toallow selection by the user of an area to be erased on the medium. Forinstance, the area to the erased may be a session, a plurality ofsessions, or the whole information zone.

When the user selects one or more session(s), the microprocessor of themicroprocessor assembly 24 recovers in the Table Of Content thelocations of the selected session(s) and drives the servo block 34accordingly. As a result, the position of the laser beam 41 iscontrolled so as to scan only the locations of the selected session(s).After one or more sessions have been erased, the Table Of Content mustbe updated so as to remove reference to the erased session(s).

In another embodiment, when the whole medium is to be erased (eitherbecause this is the option selected by the user, or because there is noother erasing option available), the microprocessor of themicroprocessor assembly 24 checks in the Table Of Content the locationsof the areas of the medium that are recorded. This information is usedto skip during the erasing process the parts of the medium that are notrecorded (the servo block 34 is instructed accordingly by themicroprocessor). This embodiment is advantageous because it leads to areduction in the amount of time required for the full erasing process(as erasing is done at low speed it is a rather long process; typicallyit may take 1 to 2 hours).

The block diagram of FIG. 3 is a schematic representation of a preferredembodiment of a method according to the invention for driving the medium1.

in box 100 the medium 1 is introduced in the device 10;

then, in box 101 the required information is recovered from the medium1, notably the ADIP information including the erasing power and theerasing linear velocity be used with the medium 1;

then, in box 102, the user is prompted to select an operating modeamongst a plurality of operating modes including a writing mode W, anerasing mode E and optionally a reading mode R;

then, in box 103, depending on the selected operating mode, enquiriesare made in the Table Of Content to determine the location(s) to bescanned;

then, in box 104, the power P and the linear velocity S are setdepending on the selected operating mode;

then, in box 105, the medium is scanned at the appropriate locationswith a laser beam having the appropriate power while the medium isrotated at the appropriate linear velocity so as to read or write orerase the medium;

then, in box 106, when applicable, the Table Of Content is updated.

With respect to the described phase change storage medium, drivingdevice and driving method, modifications or improvements may be proposedwithout departing from the scope of the invention. The invention is thusnot limited to the examples provided, in particular it is not limited tothe DVD+R standard.

In the embodiment described with reference to FIG. 2, the wobble is amodulated signal used to carry location information but not fortracking. This is not restrictive. The wobble signal can also be usedfor tracking as an alternative to the known “one-spot push-pull” or“3-spots push-pull” methods. The invention is applicable independentlyon the type of wobble signal (pure periodic or modulated wobble signal)and independently on the way the wobble signal is used (used fortracking and/or carrying information). When the wobble is not modulated,then the information regarding the power and linear velocity to be usedhave to be located in the information zone of the medium.

The embodiment of FIG. 2 uses a four-quadrant photo-detector. This isnot restrictive. For instance a two-segments photo-detector having adividing line running parallel to the direction of the tracks to bescanned can be used instead of a four-quadrant photo-detector.

The use of the word “comprise” does not exclude the presence of otherelements or steps than those listed in the claims or in the description.

1. A device (10) for driving a phase-change medium (1) having a layer(6) made of a material capable of changing locally between an amorphousstate and a crystalline state, said material been characterized by amaximum crystalline velocity above which change from said amorphousstate to said crystalline state cannot be achieved, said devicecomprising: a user interface (26) through which a user can select anoperating mode amongst a plurality of operating modes including awriting mode for writing data on said medium by locally changing saidmaterial from said crystalline state to said amorphous state and anerasing mode for erasing data written on said medium by locally changingsaid material back from said amorphous state to said crystalline state,means for producing a laser beam for scanning said medium, means (40)for controlling the power of said laser beam depending on the selectedoperating mode, and means (72) for rotating said medium at a linearvelocity that depends on the selected operating mode, the linearvelocity applied in said writing mode being much higher than saidmaximum crystalline velocity, and the linear velocity applied in saiderasing mode being equal to or lower than said maximum crystallinevelocity.
 2. A device as claimed in claim 1, wherein said user interfaceis further designed so as to allow selection of a reading mode forreading the data written on said medium.
 3. A device as claimed in claim1, comprising means for reading on said medium the value of the powerand the linear velocity to be used in said erasing mode.
 4. A device asclaimed in claim 1 wherein said user interface is designed so as toallow the user for selecting an area of data to be erased on saidmedium, said device comprising means (34) for controlling the positionof said laser beam so as to scan only said area of data in said erasingmode.
 5. A device as claimed in claim 4, comprising means fordetermining the location on said medium of said area of data by lookingsaid location up in a list of recorded-areas stored on said medium, andmeans for removing said area of data from said list of recorded-areasafter said area of data was erased.
 6. A device as claimed in claim 1,comprising means for determining the area(s) of the medium where dataare written, and means for controlling the position of said laser beamso as to scan only said area(s) of data in said erasing mode.
 7. Aphase-change medium having: a) a layer made of a material capable ofchanging locally between an amorphous state and a crystalline state whenheated by a laser having an appropriate power while said medium isrotated at an appropriate linear velocity, said material beencharacterized by a maximum crystalline velocity above which change fromsaid amorphous state to said crystalline state cannot be achieved, b) awobbled track which wobbling carries medium-related information, saidmedium-related information comprising the value of: the power and thelinear velocity, referred to as writing power and writing linearvelocity, to be used for locally changing said material from saidcrystalline state to said amorphous state, the power and the linearvelocity, referred to as erasing power and erasing linear velocity, tobe used for locally changing said material from said amorphous state tosaid crystalline state, wherein said writing linear velocity is muchhigher than said maximum crystalline velocity and said erasing linearvelocity is not higher than said maximum crystalline velocity.
 8. Amethod for driving of a phase change medium having a layer made of amaterial capable of changing locally between an amorphous state and acrystalline state, said material been characterized by a maximumcrystalline velocity above which change from said amorphous state tosaid crystalline state cannot be achieved, said method comprising thesteps of: reading a user selection amongst a plurality of availableoperating modes including a writing mode for writing data on said mediumby locally changing said material from said crystalline state to saidamorphous state and an erasing mode for erasing data written on saidmedium by locally changing said material back from said amorphous stateto said crystalline state, producing a laser beam for scanning saidmedium, controlling the power of said laser beam depending on theselected operating mode, and rotating said medium at a linear velocitythat depends on the selected operating mode, the linear velocity appliedin said writing mode being much higher than said maximum crystallinevelocity, and the linear velocity applied in said erasing mode beingequal to or lower than said maximum crystalline velocity.